Population genetic analysis and sub-structuring of Theileria parva in the northern and eastern parts of Zambia

Tick-Borne Diseases in Sub-Saharan Africa: A Systematic Review of Pathogens, Research Focus, and Implications for Public Health

Sub-Saharan Africa, with its hot and humid climate, is a conducive zone for tick proliferation. These vectors pose a major challenge to both animal and human health in the region. However, despite the relevance of emerging diseases and evidence of tick-borne disease emergence, very few studies have been dedicated to investigating zoonotic pathogens transmitted by ticks in this area. To raise awareness of the risks of tick-borne zoonotic diseases in sub-Saharan Africa, and to define a direction for future research, this systematic review considers the trends of research on tick-borne bacteria, parasites, and viruses from 2012 to 2023, aiming to highlight the circulation of these pathogens in ticks, cattle, sheep, goats, and humans. For this purpose, three international databases were screened to select 159 papers fitting designed inclusion criteria and used for qualitative analyses. Analysis of these studies revealed a high diversity of tick-borne pathogens in sub-Saharan Africa, with a total of 37 bacterial species, 27 parasite species, and 14 viruses identified. Among these, 27% were zoonotic pathogens, yet only 11 studies investigated their presence in humans. Furthermore, there is growing interest in the investigation of bacteria and parasites in both ticks and ruminants. However, research into viruses is limited and has only received notable interest from 2021 onwards. While studies on the detection of bacteria, including those of medical interest, have focused on ticks, little consideration has been given to these vectors in studies of parasites circulation. Regarding the limited focus on zoonotic pathogens transmitted by ticks, particularly in humans, despite documented cases of emerging zoonoses and the notable 27% proportion reported, further efforts should be made to fill these gaps. Future studies should prioritize the investigation of zoonotic pathogens, especially viruses, which represent the primary emerging threats, by adopting a One Health approach. This will enhance the understanding of their circulation and impact on both human and animal health. In addition, more attention should be given to the risk factors/drivers associated to their emergence as well as the perception of the population at risk of infection from these zoonotic pathogens.

p67 gene alleles sequence analysis reveals Theileria parva parasites associated with East Coast fever and Corridor disease in buffalo from Zambia

Theileriosis caused by Theileria parva infections is responsible for high cattle mortalities in Zambia. Although infected buffalo are a risk to cattle, the characterization of T. parva parasites occurring in this host in Zambia has not been reported. Furthermore, considering the advances in the development of a p67 subunit vaccine, the knowledge of p67 genetic and antigenic diversity in both cattle and buffalo associated T. parva is crucial. Therefore, blood samples from buffalo (n=43) from Central, Eastern and Southern provinces, and cattle (n=834) from Central, Copperbelt, Eastern, Lusaka, and Southern provinces, were tested for T. parva infection and the parasites characterized by sequencing the gene encoding the p67 antigen. About 76.7 % of buffalo and 19.3 % of cattle samples were PCR positive for T. parva. Three of the four known p67 allele types (1, 2 and 3) were identified in parasites from buffalo, of which two (allele types 2 and 3) are associated with T. parva parasites responsible for Corridor disease. Only allele type 1, associated with East Coast fever, was identified from cattle samples, consistent with previous reports from Zambia. Phylogenetic analysis revealed segregation between allele type 1 sequences from cattle and buffalo samples as they grouped separately within the same sub-clade. The high occurrence of T. parva infection in buffalo samples investigated demonstrates the risk of Corridor disease infection, or even outbreaks, should naïve cattle co-graze with infected buffalo in the presence of the tick vector. In view of a subunit vaccine, the antigenic diversity in buffalo associated T. parva should be considered to ensure broad protection. The current disease control measures in Zambia may require re-evaluation to ensure that cattle are protected against buffalo-derived T. parva infections. Parasite stocks used in 'infection and treatment' immunization in Zambia, have not been evaluated for protection against buffalo-derived T. parva parasites currently circulating in the buffalo population.

In vitro efficacy of plumbagin and thymol against Theileria annulata

Phytochemical compounds, plumbagin and thymol were evaluated for their efficacy against Theileria annulata using MTT cell viability assay. Plumbagin and thymol were found to be effective in preventing the proliferation of Theileria annulata infected bovine lymphocytes. The IC50 values of plumbagin and thymol were 0.019 µM and 0.009 µM, respectively. Plumbagin and thymol were found to be non-cytotoxic to the bovine peripheral blood mononuclear cells. However, both the compounds were found to have inhibitory effect on vero cell proliferation. Plumbagin had primarily anti-theilerial activity but thymol had primarily anti-mitotic activity. The in vitro efficacy and cell toxicity studies indicate the potential application of plumbagin, purified from Plumbago indica as a lead therapeutic molecule against T. annulata infection in cattle.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s12639-022-01550-x.

Epidemiology of Ticks and Tick-Borne Pathogens in Domestic Ruminants across Southern African Development Community (SADC) Region from 1980 until 2021: A Systematic Review and Meta-Analysis

Ticks are hematophagous ectoparasites that are capable of infesting a wide range of mammals, including domestic animals, ruminants, wildlife, and humans across the world, and they transmit disease-causing pathogens. Numerous individual epidemiological studies have been conducted on the distribution and prevalence of ticks and tick-borne diseases (TBDs) in the Southern African Developing Community (SADC) region, but no effort has been undertaken to synchronize findings, which would be helpful in the implementation of consolidated tick control measures. With the aim of generating consolidated pooled prevalence estimates of ticks and TBDs in the SADC region, we performed a systematic review and meta-analysis of published articles using the PRISMA 2020 guidelines. A deep search was performed on five electronic databases, namely, PubMed, ScienceDirect, Google Scholar, AJOL, and Springer Link. Of the 347 articles identified, only 61 of the articles were eligible for inclusion. In total, 18,355 tick specimens were collected, belonging to the genera Amblyomma, Haemaphysalis, Hyalomma, and Rhipicephalus (including Boophilus) across several countries, including South Africa (n = 8), Tanzania (n = 3), Zambia (n = 2), Zimbabwe (n = 2), Madagascar (n = 2), Angola (n = 2), Mozambique (n = 1), and Comoros (n = 1). The overall pooled prevalence estimate (PPE) of TBPs in livestock was 52.2%, with the highest PPE in cattle [51.2%], followed by sheep [45.4%], and goats [29.9%]. For bacteria-like and rickettsial TBPs, Anaplasma marginale had the highest PPE of 45.9%, followed by A. centrale [14.7%], A. phagocytophilum [2.52%], and A. bovis [0.88%], whilst Ehrlichia ruminantium had a PPE of 4.2%. For piroplasmids, Babesia bigemina and B. bovis had PPEs of 20.8% and 20.3%, respectively. Theileria velifera had the highest PPE of 43.0%, followed by T. mutans [29.1%], T. parva [25.0%], and other Theileria spp. [14.06%]. Findings from this study suggest the need for a consolidated scientific approach in the investigation of ticks, TBPs, and TBDs in the whole SADC region, as most of the TBDs are transboundary and require a regional control strategy.

Detection of Tick-Borne Bacterial and Protozoan Pathogens in Ticks from the Zambia–Angola Border

Tick-borne diseases (TBDs), including emerging and re-emerging zoonoses, are of public health importance worldwide; however, TBDs tend to be overlooked, especially in countries with fewer resources, such as Zambia and Angola. Here, we investigated Rickettsia, Anaplasmataceae, and Apicomplexan pathogens in 59 and 96 adult ticks collected from dogs and cattle, respectively, in Shangombo, a town at the Zambia–Angola border. We detected Richkettsia africae and Rickettsia aeschilimannii in 15.6% of Amblyomma variegatum and 41.7% of Hyalomma truncatum ticks, respectively. Ehrlichia minasensis was detected in 18.8% of H. truncatum, and Candidatus Midichloria mitochondrii was determined in Hyalomma marginatum. We also detected Babesia caballi and Theileria velifera in A. variegatum ticks with a 4.4% and 6.7% prevalence, respectively. In addition, Hepatozoon canis was detected in 6.5% of Rhipicephalus lunulatus and 4.3% of Rhipicephalus sanguineus. Coinfection of R. aeshilimannii and E. minasensis were observed in 4.2% of H. truncatum. This is the first report of Ca. M. mitochondrii and E. minasensis, and the second report of B. caballi, in the country. Rickettsia africae and R. aeschlimannii are pathogenic to humans, and E. minasensis, B. caballi, T. velifera, and H. canis are pathogenic to animals. Therefore, individuals, clinicians, veterinarians, and pet owners should be aware of the distribution of these pathogens in the area.

Genotyping of Theileria parva populations in vaccinated and non-vaccinated cattle in Malawi

Theileria parva is an apicomplexan protozoan parasite that causes bovine theileriosis (East Coast Fever; ECF) in central, eastern and southern Africa. In Malawi, ECF is endemic in the northern and central regions where it has negatively affected the development of dairy industry. Despite its endemic status the genetic population structure of T. parva in Malawi is currently unknown. To obtain an understanding of T. parva in Malawi, we performed population genetics analysis of T. parva populations in cattle vaccinated with the Muguga cocktail live vaccine and non-vaccinated cattle using mini- and microsatellite markers covering all the four T. parva chromosomes. The T. parva Muguga strain was included in this study as a reference strain. Linkage disequilibrium was observed when all samples were treated as a single population. There was sub-structuring among the samples as shown by the principal coordinate analysis. Majority of the samples clustered with the T. parva Muguga reference strain suggesting that the isolates in Malawi are closely related to the vaccine component, which support the current use of Muguga cocktail vaccine to control ECF. The clustering of samples from non-endemic southern region with those from endemic central region suggests expansion of the distribution of T. parva in Malawi.

Sequence Diversity of Tp1 and Tp2 Antigens and Population Genetic Analysis of Theileria parva in Unvaccinated Cattle in Zambia's Chongwe and Chisamba Districts

East Coast Fever (ECF), caused by Theileria parva, is a major constraint to improved livestock keeping in east and central Africa, including Zambia. To understand the dynamics and determine the candidates for immunization in Zambia's Chongwe and Chisamba districts, a combination of Tp1 and Tp2 gene sequencing and microsatellite analysis using nine markers was conducted from which an abundance of Muguga, Kiambu, Serengeti and Katete epitopes in the field samples was obtained. Phylogenetic analysis showed six (Tp1) and three (Tp2) clusters with an absence of geographical origin clustering. The majority of haplotypes were related to Muguga, Kiambu, Serengeti and Katete, and only a few were related to Chitongo. Both antigens showed purifying selection with an absence of positive selection sites. Furthermore, low to moderate genetic differentiation was observed among and within the populations, and when vaccine stocks were compared with field samples, Chongwe samples showed more similarity to Katete and less to Chitongo, while Chisamba samples showed similarity to both Katete and Chitongo and not to Muguga, Kiambu or Serengeti. We conclude that the use of Katete stock for immunization trials in both Chongwe and Chisamba districts might produce desirable protection against ECF.

Molecular characterization and population genetics of Theileria parva in Burundi's unvaccinated cattle: Towards the introduction of East Coast fever vaccine

Theileria parva (T. parva) is a protozoan parasite that causes East Coast fever (ECF). The disease is endemic in Burundi and is a major constraint to livestock development. In this study, the parasite prevalence in cattle in six regions namely; Northern, Southern, Eastern, Western, Central and North Eastern was estimated. Furthermore, the sequence diversity of p67, Tp1 and Tp2 genes was assessed coupled with the population genetic structure of T. parva using five satellite markers. The prevalence of ECF was 30% (332/1109) on microscopy, 60% (860/1431) on ELISA and 79% (158/200) on p104 gene PCR. Phylogenetic analysis of p67 gene revealed that only allele 1 was present in the field samples. Furthermore, phylogenetic analysis of Tp1 and Tp2 showed that the majority of samples clustered with Muguga, Kiambu and Serengeti and shared similar epitopes. On the other hand, genetic analysis revealed that field samples shared only two alleles with Muguga Cocktail. The populations from the different regions indicated low genetic differentiation (FST = 0.047) coupled with linkage disequilibrium and non-panmixia. A low to moderate genetic differentiation (FST = 0.065) was also observed between samples and Muguga cocktail. In conclusion, the data presented revealed the presence of a parasite population that shared similar epitopes with Muguga Cocktail and was moderately genetically differentiated from it. Thus, use of Muguga Cocktail vaccine in Burundi is likely to confer protection against T. parva in field challenge trials.

Population Genetic Analysis of the Theileria annulata Parasites Identified Limited Diversity and Multiplicity of Infection in the Vaccine From India

Background: Apicomplexan parasite Theileria annulata causes significant economic loss to the livestock industry in India and other tropical countries. In India, parasite control is mainly dependent on the live attenuated schizont vaccine and the drug buparvaquone. For effective disease control, it is essential to study the population structure and genetic diversity of the Theileria annulata field isolates and vaccine currently used in India. Methodology/Results: A total of 125 T. annulata isolates were genotyped using 10 microsatellite markers from four states belonging to different geographical locations of India. Limited genetic diversity was observed in the vaccine isolates when compared to the parasites in the field; a level of geographical substructuring was evident in India. The number of genotypes observed per infection was highest in India when compared to other endemic countries, suggesting high transmission intensity and abundance of ticks in the country. A reduced panel of four markers can be used for future studies in these for surveillance of the T. annulata parasites in India. Conclusion: High genetic variation between the parasite populations in the country suggests their successful spread in the field and could hamper the disease control programs. Our findings provide the baseline data for the diversity and population structure of T. annulata parasites from India. The low diversity in the vaccine advocates improving the current vaccine, possibly by increasing its heterozygosity. The reduced panel of the markers identified in this study will be helpful in monitoring parasite and its reintroduction after Theileria eradication.

Investigation of the piroplasm diversity circulating in wildlife and cattle of the greater Kafue ecosystem, Zambia

Background

Piroplasms are vector-borne intracellular hemoprotozoan parasites that infect wildlife and livestock. Wildlife species are reservoir hosts to a diversity of piroplasms and play an important role in the circulation, maintenance and evolution of these parasites. The potential for likely spillover of both pathogenic and non-pathogenic piroplasm parasites from wildlife to livestock is underlined when a common ecological niche is shared in the presence of a competent vector.

Method

To investigate piroplasm diversity in wildlife and the cattle population of the greater Kafue ecosystem, we utilized PCR to amplify the 18S rRNA V4 hyper-variable region and meta-barcoding strategy using the Illumina MiSeq sequencing platform and amplicon sequence variant (ASV)-based bioinformatics pipeline to generate high-resolution data that discriminate sequences down to a single nucleotide difference.

Results

A parasite community of 45 ASVs corresponding to 23 species consisting of 4 genera of Babesia, Theileria, Hepatozoon and Colpodella, were identified in wildlife and the cattle population from the study area. Theileria species were detected in buffalo, impala, hartebeest, sable antelope, sitatunga, wild dog and cattle. In contrast, Babesia species were only observed in cattle and wild dog. Our results demonstrate possible spillover of these hemoprotozoan parasites from wildlife, especially buffalo, to the cattle population in the wildlife-livestock interface.

Conclusion

We demonstrated that the deep amplicon sequencing of the 18S rRNA V4 hyper-variable region for wildlife was informative. Our results illustrated the diversity of piroplasma and the specificity of their hosts. They led us to speculate a possible ecological cycle including transmission from wildlife to domestic animals in the greater Kafue ecosystem. Thus, this approach may contribute to the establishment of appropriate disease control strategies in wildlife-livestock interface areas.

Sequence diversity of cytotoxic T cell antigens and satellite marker analysis of Theileria parva informs the immunization against East Coast fever in Rwanda

Background

East Coast fever (ECF) caused by Theileria parva is endemic in Rwanda. In this study, the antigenic and genetic diversity of T. parva coupled with immunization and field challenge were undertaken to provide evidence for the introduction of ECF immunization in Rwanda.

Methods

Blood collected from cattle in the field was screened for T. parva using ELISA and PCR targeting the p104 gene. Tp1 and Tp2 gene sequences were generated from field samples and from Gikongoro and Nyakizu isolates. Furthermore, multilocus genotype data was generated using 5 satellite markers and an immunization challenge trial under field conditions using Muguga cocktail vaccine undertaken.

Results

Out of 120 samples, 44 and 20 were positive on ELISA and PCR, respectively. Antigenic diversity of the Tp1 and Tp2 gene sequences revealed an abundance of Muguga, Kiambu and Serengeti epitopes in the samples. A further three clusters were observed on both Tp1 and Tp2 phylogenetic trees; two clusters comprising of field samples and vaccine isolates and the third cluster comprising exclusively of Rwanda samples. Both antigens exhibited purifying selection with no positive selection sites. In addition, satellite marker analysis revealed that field samples possessed both shared alleles with Muguga cocktail on all loci and also a higher proportion of unique alleles. The Muguga cocktail (Muguga, Kiambu and Serengeti) genotype compared to other vaccine isolates, was the most represented in the field samples. Further low genetic sub-structuring (F_ST = 0.037) coupled with linkage disequilibrium between Muguga cocktail and the field samples was observed. Using the above data to guide a field immunization challenge trial comprising 41 immunized and 40 control animals resulted in 85% seroconversion in the immunized animals and an efficacy of vaccination of 81.7%, implying high protection against ECF.

Conclusions

Antigenic and genetic diversity analysis of T. parva facilitated the use of Muguga cocktail vaccine in field conditions. A protection level of 81.7% was achieved, demonstrating the importance of combining molecular tools with field trials to establish the suitability of implementation of immunization campaigns. Based on the information in this study, Muguga cocktail immunization in Rwanda has a potential to produce desirable results.

Antigen gene and variable number tandem repeat (VNTR) diversity in Theileria parva parasites from Ankole cattle in south-western Uganda: Evidence for conservation in antigen gene sequences combined with extensive polymorphism at VNTR loci

Theileria parva is a tick-transmitted apicomplexan protozoan parasite that infects lymphocytes of cattle and African Cape buffalo (Syncerus caffer), causing a frequently fatal disease of cattle in eastern, central and southern Africa. A live vaccination procedure, known as infection and treatment method (ITM), the most frequently used version of which comprises the Muguga, Serengeti-transformed and Kiambu 5 stocks of T. parva, delivered as a trivalent cocktail, is generally effective. However, it does not always induce 100% protection against heterologous parasite challenge. Knowledge of the genetic diversity of T. parva in target cattle populations is therefore important prior to extensive vaccine deployment. This study investigated the extent of genetic diversity within T. parva field isolates derived from Ankole (Bos taurus) cattle in south-western Uganda using 14 variable number tandem repeat (VNTR) satellite loci and the sequences of two antigen-encoding genes that are targets of CD8+T-cell responses induced by ITM, designated Tp1 and Tp2. The findings revealed a T. parva prevalence of 51% confirming endemicity of the parasite in south-western Uganda. Cattle-derived T. parva VNTR genotypes revealed a high degree of polymorphism. However, all of the T. parva Tp1 and Tp2 alleles identified in this study have been reported previously, indicating that they are widespread geographically in East Africa and highly conserved.

Microsatellite and minisatellite genotyping of Theileria parva population from southern Africa reveals possible discriminatory allele profiles with parasites from eastern Africa

The control of Theileria parva, a protozoan parasite that threatens almost 50% of the cattle population in Africa, is still a challenge in many affected countries. Theileria parva field parasites from eastern Africa, and parasites comprising the current live T. parva vaccine widely deployed in the same region have been reported to be genotypically diverse. However, similar reports on T. parva parasites from southern Africa are limited, especially in Corridor disease designated areas. Establishing the extent of genetic exchange in T. parva populations is necessary for effective control of the parasite infection. Twelve polymorphic microsatellite and minisatellite loci were targeted for genotypic and population genetics analysis of T. parva parasites from South Africa, Mozambique, Kenya and Uganda using genomic DNA prepared from cattle and buffalo blood samples. The results revealed genotypic similarities among parasites from the two regions of Africa, with possible distinguishing allelic profiles on three loci (MS8, MS19 and MS33) for parasites associated with Corridor disease in South Africa, and East Coast fever in eastern Africa. Individual populations were in linkage equilibrium (V_D<L), but when considered as one combined population, linkage disequilibrium (V_D>L) was observed. Genetic divergence was observed to be more within (AMOVA = 74%) than between (AMOVA = 26%) populations. Principal coordinate analysis showed clustering that separated buffalo-derived from cattle-derived T. parva parasites, although parasites from cattle showed a close genetic relationship. The results also demonstrated geographic sub-structuring of T. parva parasites based on the disease syndromes caused in cattle in the two regions of Africa. These findings provide additional information on the genotypic diversity of T. parva parasites from South Africa, and reveal possible differences based on three loci (MS8, MS19 and MS33) and similarities between buffalo-derived T. parva parasites from southern and eastern Africa.

Genetic Diversity and Sequence Polymorphism of Two Genes Encoding Theileria parva Antigens Recognized by CD8+ T Cells among Vaccinated and Unvaccinated Cattle in Malawi

East Coast fever (ECF) is an acute fatal tick-borne disease of cattle caused by Theileria parva. It causes major losses in exotic and crossbreed cattle, but this could be prevented by a vaccine of T. parva if the vaccine is selected properly based on information from molecular epidemiology studies. The Muguga cocktail (MC) vaccine (Muguga, Kiambu 5 and Serengeti-transformed strains) has been used on exotic and crossbreed cattle. A total of 254 T. parva samples from vaccinated and unvaccinated cattle were used to understand the genetic diversity of T. parva in Malawi using partial sequences of the Tp1 and Tp2 genes encoding T. parva CD8⁺ antigens, known to be immunodominant and current candidate antigens for a subunit vaccine. Single nucleotide polymorphisms were observed at 14 positions (3.65%) in Tp1 and 156 positions (33.12%) in Tp2, plus short deletions in Tp1, resulting in 6 and 10 amino acid variants in the Tp1 and Tp2 genes, respectively. Most sequences were either identical or similar to T. parva Muguga and Kiambu 5 strains. This may suggest the possible expansion of vaccine components into unvaccinated cattle, or that a very similar genotype already existed in Malawi. This study provides information that support the use of MC to control ECF in Malawi.

Genetic and antigenic variation of the bovine tick-borne pathogen Theileria parva in the Great Lakes region of Central Africa

Background

Theileria parva causes East Coast fever (ECF), one of the most economically important tick-borne diseases of cattle in sub-Saharan Africa. A live immunisation approach using the infection and treatment method (ITM) provides a strong long-term strain-restricted immunity. However, it typically induces a tick-transmissible carrier state in cattle and may lead to spread of antigenically distinct parasites. Thus, understanding the genetic composition of T. parva is needed prior to the use of the ITM vaccine in new areas. This study examined the sequence diversity and the evolutionary and biogeographical dynamics of T. parva within the African Great Lakes region to better understand the epidemiology of ECF and to assure vaccine safety. Genetic analyses were performed using sequences of two antigen-coding genes, Tp1 and Tp2, generated among 119 T. parva samples collected from cattle in four agro-ecological zones of DRC and Burundi.

Results

The results provided evidence of nucleotide and amino acid polymorphisms in both antigens, resulting in 11 and 10 distinct nucleotide alleles, that predicted 6 and 9 protein variants in Tp1 and Tp2, respectively. Theileria parva samples showed high variation within populations and a moderate biogeographical sub-structuring due to the widespread major genotypes. The diversity was greater in samples from lowlands and midlands areas compared to those from highlands and other African countries. The evolutionary dynamics modelling revealed a signal of selective evolution which was not preferentially detected within the epitope-coding regions, suggesting that the observed polymorphism could be more related to gene flow rather than recent host immune-based selection. Most alleles isolated in the Great Lakes region were closely related to the components of the trivalent Muguga vaccine.

Conclusions

Our findings suggest that the extensive sequence diversity of T. parva and its biogeographical distribution mainly depend on host migration and agro-ecological conditions driving tick population dynamics. Such patterns are likely to contribute to the epidemic and unstable endemic situations of ECF in the region. However, the fact that ubiquitous alleles are genetically similar to the components of the Muguga vaccine together with the limited geographical clustering may justify testing the existing trivalent vaccine for cross-immunity in the region.

Theileria lestoquardi in Sudan is highly diverse and genetically distinct from that in Oman

Malignant ovine theileriosis is a severe tick-borne protozoan disease of sheep and other small ruminants which is widespread in sub-Saharan Africa and the Middle East. The disease is of considerable economic importance in Sudan as the export of livestock provides a major contribution to the gross domestic product of this country. Molecular surveys have demonstrated a high prevalence of sub-clinical infections of Theileria lestoquardi, the causative agent, among small ruminants. No information is currently available on the extent of genetic diversity and genetic exchange among parasites in different areas of the country. The present study used a panel of T. lestoquardi specific micro- and mini-satellite genetic markers to assess diversity of parasites in Sudan (Africa) and compared it to that of the parasite population in Oman (Asia). A moderate level of genetic diversity was observed among parasites in Sudan, similar to that previously documented among parasites in Oman. However, a higher level of mixed-genotype infection was identified in Sudanese animals compared to Omani animals, consistent with a higher rate of tick transmission. In addition, the T. lestoquardi genotypes detected in these two countries form genetically distinct groups. The results of this work highlight the need for analysis of T. lestoquardi populations in other endemic areas in the region to inform on novel approaches for controlling malignant theileriosis.

Population Genetic Analysis of Theileria annulata from Six Geographical Regions in China, Determined on the Basis of Micro- and Mini-satellite Markers

Theileria annulata, a tick-borne apicomplexan protozoan, causes a lymphoproliferative disease of cattle with high prevalence in tropical and sub-tropical regions. Understanding the genetic diversity and structure of local populations will provide more fundamental knowledge for the population genetics and epidemics of protozoa. In this study, 78 samples of T. annulata collected from cattle/yaks representing 6 different geographic populations in China were genotyped using eight micro- and mini-satellite markers. High genetic variation within population, moderate genetic differentiation, and high level of diversity co-occurring with significant linkage disequilibrium were observed, which indicates there is gene flow between these populations in spite of the existence of reproductive and geographical barriers among populations. Furthermore, some degree of genetic differentiation was also found between samples from China and Oman. These findings provide a first glimpse of the genetic diversity of the T. annulata populations in China, and might contribute to the knowledge of distribution, dynamics, and epidemiology of T. annulata populations and optimize the management strategies for control.

Application of system dynamics and participatory spatial group model building in animal health: A case study of East Coast Fever interventions in Lundazi and Monze districts of Zambia

East Coast Fever (ECF) is the most economically important production disease among traditional beef cattle farmers in Zambia. Despite the disease control efforts by the government, donors, and farmers, ECF cases are increasing. Why does ECF oscillate over time? Can alternative approaches such as systems thinking contribute solutions to the complex ECF problem, avoid unintended consequences, and achieve sustainable results? To answer these research questions and inform the design and implementation of ECF interventions, we qualitatively investigated the influence of dynamic socio-economic, cultural, and ecological factors. We used system dynamics modelling to specify these dynamics qualitatively, and an innovative participatory framework called spatial group model building (SGMB). SGMB uses participatory geographical information system (GIS) concepts and techniques to capture the role of spatial phenomenon in the context of complex systems, allowing stakeholders to identify spatial phenomenon directly on physical maps and integrate such information in model development. Our SGMB process convened focus groups of beef value chain stakeholders in two distinct production systems. The focus groups helped to jointly construct a series of interrelated system dynamics models that described ECF in a broader systems context. Thus, a complementary objective of this study was to demonstrate the applicability of system dynamics modelling and SGMB in animal health. The SGMB process revealed policy leverage points in the beef cattle value chain that could be targeted to improve ECF control. For example, policies that develop sustainable and stable cattle markets and improve household income availability may have positive feedback effects on investment in animal health. The results obtained from a SGMB process also demonstrated that a “one-size-fits-all” approach may not be equally effective in policing ECF in different agro-ecological zones due to the complex interactions of socio-ecological context with important, and often ignored, spatial patterns.

Theileria lestoquardi displays reduced genetic diversity relative to sympatric Theileria annulata in Oman

The Apicomplexan parasites, Theileria lestoquardi and Theileria annulata, the causative agents of theileriosis in small and large ruminants, are widespread in Oman, in areas where cattle, sheep and goats co-graze. Genetic analysis can provide insight into the dynamics of the parasite and the evolutionary relationship between species. Here we identified ten genetic markers (micro- and mini-satellites) spread across the T. lestoquardi genome, and confirmed their species specificity. We then genotyped T. lestoquardi in different regions in Oman. The genetic structures of T. lestoquardi populations were then compared with previously published data, for comparable panels of markers, for sympatric T. annulata isolates. In addition, we examined two antigen genes in T. annulata (Tams1 and Ta9) and their orthologues in T. lestoquardi (Tlms1 and Tl9). The genetic diversity and multiplicity of infection (MOI) were lower in T. lestoquardi (He=0.64-0.77) than T. annulata (He=0.83-0.85) in all populations. Very limited genetic differentiation was found among T. lestoquardi and T. annulata populations. In contrast, limited but significant linkage disequilibrium was observed within regional populations of each species. We identified eight T. annulata isolates in small ruminants; the diversity and MOI were lower among ovine/caprine compared to bovine. Sequence diversity of the antigen genes, Tams1 and Ta9 in T. annulata (π=0.0733 and π=0.155 respectively), was 10-fold and 3-fold higher than the orthologous Tlms1 and Tl9 in T. lestoquardi (π=0.006 and π=0.055, respectively). Despite a comparably high prevalence, T. lestoquardi has lower genetic diversity compared to sympatric T. annulata populations. There was no evidence of differentiation among populations of either species. In comparison to T. lestoquardi, T. annulata has a larger effective population size. While genetic exchange and recombination occur in both parasite species, the extent of diversity, overall, is less for T. lestoquardi. It is, therefore, likely that T. lestoquardi evolved from an ancestor of present day T. annulata and that this occurred either once or on a limited number of occasions.

Population genetic analysis of Theileria parva isolated in cattle and buffaloes in Tanzania using minisatellite and microsatellite markers

A population genetic study of Theileria parva was conducted on 103 cattle and 30 buffalo isolates from Kibaha, Lushoto, Njombe Districts and selected National parks in Tanzania. Bovine blood samples were collected from these study areas and categorized into 5 populations; Buffalo, Cattle which graze close to buffalo, Kibaha, Lushoto and Njombe. Samples were tested by nested PCR for T. parva DNA and positives were compared for genetic diversity to the T. parva Muguga vaccine reference strain, using 3micro and 11 minisatellite markers selected from all 4 chromosomes of the parasite genome. The diversity across populations was determined by the mean number of different alleles, mean number of effective alleles, mean number of private allele and expected heterozygosity. The mean number of allele unique to populations for Cattle close to buffalo, Muguga, Njombe, Kibaha, Lushoto and Buffalo populations were 0.18, 0.24, 0.63, 0.71, 1.63 and 3.37, respectively. The mean number of different alleles ranged from 6.97 (Buffalo) to 0.07 (Muguga). Mean number of effective alleles ranged from 4.49 (Buffalo) to 0.29 (Muguga). The mean expected heterozygosity were 0.07 0.29, 0.45, 0.48, 0.59 and 0.64 for Muguga, cattle close to buffalo, Kibaha, Njombe, Lushoto and Buffalo populations, respectively. The Buffalo and Lushoto isolates possessed a close degree of diversity in terms of mean number of different alleles, effective alleles, private alleles and expected heterozygosity. The study revealed more diversity in buffalo isolates and further studies are recommended to establish if there is sharing of parasites between cattle and buffaloes which may affect the effectiveness of the control methods currently in use.

Tageldin M, Weir W, Al-Fahdi A, Johnson EH, Bobade P, Alqamashoui B, Beja-Pereira A, Thompson J, Kinnaird J, Shiels B, Tait A, Babiker H. Genetic Diversity and Population Structure of Theileria annulata in Oman

Background

Theileriosis, caused by a number of species within the genus Theileria, is a common disease of livestock in Oman. It is a major constraint to the development of the livestock industry due to a high rate of morbidity and mortality in both cattle and sheep. Since little is currently known about the genetic diversity of the parasites causing theileriosis in Oman, the present study was designed to address this issue with specific regard to T. annulata in cattle.

Methods

Blood samples were collected from cattle from four geographically distinct regions in Oman for genetic analysis of the Theileria annulata population. Ten genetic markers (micro- and mini-satellites) representing all four chromosomes of T. annulata were applied to these samples using a combination of PCR amplification and fragment analysis. The resultant genetic data was analysed to provide a first insight into the structure of the T. annulata population in Oman.

Results

We applied ten micro- and mini-satellite markers to a total of 310 samples obtained from different regions (174 [56%] from Dhofar, 68 [22%] from Dhira, 44 [14.5%] from Batinah and 24 [8%] from Sharqia). A high degree of allelic diversity was observed among the four parasite populations. Expected heterozygosity for each site ranged from 0.816 to 0.854. A high multiplicity of infection was observed in individual hosts, with an average of 3.3 to 3.4 alleles per locus, in samples derived from Batinah, Dhofar and Sharqia regions. In samples from Dhira region, an average of 2.9 alleles per locus was observed. Mild but statistically significant linkage disequilibrium between pairs of markers was observed in populations from three of the four regions. In contrast, when the analysis was performed at farm level, no significant linkage disequilibrium was observed. Finally, no significant genetic differentiation was seen between the four populations, with most pair-wise F_ST values being less than 0.03. Slightly higher F_ST values (G_ST’ = 0.075, θ = 0.07) were detected when the data for T. annulata parasites in Oman was compared with that previously generated for Turkey and Tunisia.

Conclusion

Genetic analyses of T. annulata samples representing four geographical regions in Oman revealed a high level of genetic diversity in the parasite population. There was little evidence of genetic differentiation between parasites from different regions, and a high level of genetic diversity was maintained within each sub-population. These findings are consistent with a high parasite transmission rate and frequent movement of animals between different regions in Oman.

Studies of trypanosomiasis in the Luangwa valley, north-eastern Zambia

Background

The present study, conducted in Zambia’s Luangwa valley where both animal African trypanosomiasis (AAT) and human African trypanosomiasis (HAT) are endemic, combined the use of microscopy and molecular techniques to determine the presence of trypanosome species in cattle, goats and tsetse flies.

Methods

This study was conducted between 2008 and 2010 in Petauke, Chama and Isoka districts, north-eastern Zambia. A total of 243 cattle, 36 goats and 546 tsetse flies, were examined for presence of trypanosome species using microscopy, PCR and loop-mediated isothermal amplification (LAMP).

Results

There was poor agreement among the test methods used for detection of trypanosomes species in animal blood and tsetse flies. Trypanosomes were observed in 6.1 % (95 % CI: 3.3-8.9 %) of the animals sampled by microscopy, 7.5 % (95 % CI: 4.4–10.6 %) by PCR and 18.6 % (95 % CI: 13.6–23.6 %) by PFR-LAMP. PFR-LAMP was more sensitive for detecting Trypanozoon than KIN-PCR. The highest occurrence of AAT was recorded in cattle from Petauke (58.7 %, 95 % CI: 44.7–72.7 %) while the lowest was from Isoka (5.4 %, 95 % CI: 0.8–10.0 %). Infection of both cattle and goats with Trypanosoma congolense and T. vivax was associated with clinical AAT.

Conclusion

When selecting molecular techniques for AAT surveillance in endemic regions, the KIN-PCR and species-specific PCR may be recommended for screening animal or tsetse fly samples for T. congolense and T. vivax, respectively. On the other hand, species-specific PCR and/or LAMP might be of greater value in the screening of animal and human body fluids as well as tsetse fly samples for Trypanozoon.

Not "out of Nantucket": Babesia microti in southern New England comprises at least two major populations

BACKGROUND

Deer tick-transmitted human babesiosis due to Babesia microti appears to be expanding its distribution and prevalence in the northeastern United States. One hypothesis for this emergence is the introduction of parasites into new sites from areas of long-standing transmission, such as Nantucket Island, Massachusetts.

METHODS

We developed a typing system based on variable number tandem repeat loci that distinguished individual B. microti genotypes. We thereby analyzed the population structure of parasites from 11 sites, representing long-standing and newly emerging transmission in southern New England (northeastern United States), and compared their haplotypes and allele frequencies to determine the most probable number of B. microti populations represented by our enzootic collections. We expected to find evidence for a point source introduction across southern New England, with all parasites clearly derived from Nantucket, the site with the most intense longstanding transmission.

RESULTS

B. microti in southern New England comprises at least two major populations, arguing against a single source. The Nantucket group comprises Martha's Vineyard, Nantucket and nearby Cape Cod. The Connecticut/Rhode Island (CT/RI) group consists of all the samples from those states along with samples from emerging sites in Massachusetts.

CONCLUSIONS

The expansion of B. microti in the southern New England mainland is not due to parasites from the nearby terminal moraine islands (Nantucket group), but rather from the CT/RI group. The development of new B. microti foci is likely due to a mix of local intensification of transmission within relict foci across southern New England as well as long distance introduction events.

Genetic and antigenic diversity of Theileria parva in cattle in Eastern and Southern zones of Tanzania. A study to support control of East Coast fever

This study investigated the genetic and antigenic diversity of Theileria parva in cattle from the Eastern and Southern zones of Tanzania. Thirty-nine (62%) positive samples were genotyped using 14 mini- and microsatellite markers with coverage of all four T. parva chromosomes. Wright's F index (F(ST) = 0 × 094) indicated a high level of panmixis. Linkage equilibrium was observed in the two zones studied, suggesting existence of a panmyctic population. In addition, sequence analysis of CD8+ T-cell target antigen genes Tp1 revealed a single protein sequence in all samples analysed, which is also present in the T. parva Muguga strain, which is a component of the FAO1 vaccine. All Tp2 epitope sequences were identical to those in the T. parva Muguga strain, except for one variant of a Tp2 epitope, which is found in T. parva Kiambu 5 strain, also a component the FAO1 vaccine. Neighbour joining tree of the nucleotide sequences of Tp2 showed clustering according to geographical origin. Our results show low genetic and antigenic diversity of T. parva within the populations analysed. This has very important implications for the development of sustainable control measures for T. parva in Eastern and Southern zones of Tanzania, where East Coast fever is endemic.

A pan-Theileria FRET-qPCR survey for Theileria spp. in ruminants from nine provinces of China

Background

Theileria spp. are tick transmitted protozoa that can infect large and small ruminants causing disease and economic losses. Diagnosis of infections is often challenging, as parasites can be difficult to detect and identify microscopically and serology is unreliable. While there are PCR assays which can identify certain Theileria spp., there is no one PCR that has been designed to identify all recognized species that occur in ruminants and which will greatly simplify the laboratory diagnoses of infections.

Methods

Primers and probes for a genus-specific pan-Theileria FRET-qPCR were selected by comparing sequences of recognized Theileria spp. in GenBank and the test validated using reference organisms. The assay was also tested on whole blood samples from large and small ruminants from nine provinces in China.

Results

The pan-Theileria FRET-qPCR detected all recognized species but none of the closely related protozoa. In whole blood samples from animals in China, Theileria spp. DNA was detected in 53.2% of the sheep tested (59/111), 44.4% of the goats (120/270) and 30.8% of the cattle (380/1,235). Water buffaloes (n = 29) were negative. Sequencing of some of the PCR products showed cattle in China were infected with T. orientalis/T. sergenti/T. buffeli group while T. ovis and T. luwenshuni were found in sheep and T. luwenshuni in goats. The prevalence of Theileria DNA was significantly higher in Bos p. indicus than in Bos p. taurus (77.7% vs. 18.3%) and copy numbers were also significantly higher (10^4.88 vs. 10^3.00Theileria 18S rRNA gene copies/per ml whole blood).

Conclusions

The pan-Theileria FRET-qPCR can detect all recognized Theileria spp. of ruminants in a single reaction. Large and small ruminants in China are commonly infected with a variety of Theileria spp.

Phylogeny and virulence divergency analyses of Toxoplasma gondii isolates from China

BACKGROUND

Toxoplasma gondii (T. gondii) is a very successful parasite that can infect virtually all warm blooded animals with a worldwide distribution. It causes a large range of clinical manifestations in both humans and domesticated animals. In addition, marked biological differences exist among T. gondii strains in the pathogenicity and geographical distribution. Molecular epidemiology studies primarily based on restriction fragment length polymorphism (RFLP) method revealed that three main types are predominant in North America and Europe, whereas other diverse genotypes are found in other parts of the world. Microsatellite (MS) as a type of genetic marker has been widely used in many organisms. Limited MS genotyping, however, to fingerprint T. gondii isolates has been reported and little is known about the MS data of the strains predominantly prevalent in China.

METHODS

Genotyping of twenty-eight Chinese T. gondii isolates were performed using 15 MS markers located on 12 different chromosomes. Results were analyzed in terms of population structure by a Bayesian statistical approach. Phylogenetic analysis was obtained from a Neighbor-Net phylogenetic network. The virulence analyses of some representative isolates were determined by inoculation of mice and cell invasion assays. The gene expressions of some virulence-associated factors (VFs) were performed by quantitative real-time PCR (qRT- PCR).

RESULTS

Three haplogroups were clustered among the 28 isolates although minor genetic differences were found within haplogroups. The majority of strains belong to one haplogroup corresponding to the previously described Chinese 1 type (ToxoDB#9). Phylogenetic networks uncovered a limited diversity of T. gondii strains and the virulence differs in the strains sharing the same genotype. No remarkable difference, however, was noted in the tested VFs except for dense granule protein3 (GRA3), which was found to have a higher expression in low virulent TgCtwh6 (Wh6) strain than that in high virulent TgCtwh3 (Wh3) strain.

CONCLUSION

The profile of microsatellite typing data from Chinese T. gondii strains revealed a limited genetic diversity and the selected VFs and phylogenetic network analyses displayed less divergence, although the strain virulence differs in the Chinese 1 type of T. gondii predominantly prevalent in China.

Geographic distribution of Theileria sp. (buffalo) and Theileria sp. (bougasvlei) in Cape buffalo (Syncerus caffer) in southern Africa: implications for speciation

Strict control measures apply to movement of buffalo in South Africa including testing for Theileria parva, the causative agent of Corridor disease in cattle. The official test is a real-time hybridization PCR assay that amplifies the 18S rRNA V4 hyper-variable region of T. parva, T. sp. (buffalo) and T. sp. (bougasvlei). Mixed infections with the latter organisms affect diagnostic sensitivity due to PCR suppression. While the incidence of mixed infections in the Corridor disease endemic region of South Africa is significant, little information is available on the specific distribution and prevalence of T. sp. (buffalo) and T. sp. (bougasvlei). Specific real-time PCR assays were developed and a total of 1211 samples known to harbour these parasites were screened. Both parasites are widely distributed in southern Africa and the incidence of mixed infections with T. parva within the endemic region is similar (∼25–50%). However, a significant discrepancy exists in regard to mixed infections of T. sp. (buffalo) and T. sp. (bougasvlei) (∼10%). Evidence for speciation between T. sp. (buffalo) and T. sp. (bougasvlei) is supported by phylogenetic analysis of the COI gene, and their designation as different species. This suggests mutual exclusion of parasites and the possibility of hybrid sterility in cases of mixed infections.